Scratch built Typhoon advice needed

[Subculture]

Gear them down around 2:1, assuming a 12v system and they’ll be fine.

[Mermod]

Well it's been a little while but after an unexpected trip to the other side of the country for a funeral I'm now back in the workshop, currently waiting on those plantery motors so im playing with bow plane retracts and looking at the drive motors, I did mention before that I have 2 st4010 820kv hobbyking motors but they seem a tad overpowered for the 60mm 7blade scimitar props I have, should I be looking at a slightly more sensible motor option but still with a bit in reserve for flank speed?

Phill.

[Subculture]

BTW, if your tanks are pulling 3.5A at 12 volts- 42 watts for a free running tank, then something is definitely out of whack. An Engel tank draws about 4-5 watts free running and around 10-12 watts when compressing air behind it at around 2-3psi. This compares very favourably with pump based systems.

O-rings will be a little higher in friction than the pneumatic cup seals Engel use, but not that much.

[Subculture]

Either will work.

[Mermod]

I'm torn between the 540 or 385 motor versions, I have a habit of overdoing things, perhaps I should go with the smaller of the two.

[Subculture]

Okay so going back over the figures I realise I made in error in the first stage of gearing, and your final ratio is taller at around 10.8:1, which would stretch the motors somewhat.

if you wanted to use the motors I linked to, then bear in mind the output shaft will be larger than your 500 motor, so the pinion will need machining or you can order a new pinion with the right bore.

The tanks will be slower to fill, estimate 25-30 seconds but should only draw a few watts free running, all assuming nothing is binding up.

[Mermod]

As is the draw kicks in a 5 amps then drops to about 3.5.
yes the spur gear is a 66t 55mm diameter, i had the second one ready for the other tank in a box of goodies, turns out i engraved the o ring details on the tank end caps plus the date when it all went onto storage, the 3rd of July 2014 which got me thinking about the o ring grease sitting in tank, stripped it all down and it kinda feels like old glue so I'm currently cleaning everything, I wouldn't mind doing away with the small fragile gear setup and putting the spur gear straight on one of those planetery units then straight onto the traxxas pinion, any suggestions?

Thanks again
Phill

[Subculture]

So you didn't mention the tooth count of the Emaxx gear, but a quick google throws up something around 65 teeth, so along with the other stage of reduction I get around 16-17:1 overall reduction giving a free running spindle speed of around 750-800RPM. That is good about the right speed and reduction.

You mentioned earlier the tanks were drawing a lot of current. What was the figure?

[Mermod]

Good point, I nipped down the workshop and poked at the large E-maxx gear that surrounds the drive nut and I think it's quite free without being loose so I think the o rings ok, I knew a guy that worked at the local hydraulics place and gave him my tubing and asked him to machine the piston and o ring groove to suit, thought it was safer than my basic machining skills :)

The next group of gears is an old electric flight gear drive for mounting on 540 motors, the small brass gear is a 9mm 14tooth that fits on the drive motor, this meshes with a nylon 25mm approx 30tooth this runs the output shaft where I mount the standard 13T rc car pinion for meshing with the previously mentioned e-maxx gear.
The 540 size motor that runs it all is an EM 407, ill quote the chart all at 12v... no load RPM 13000 Amps .470 AT Maximum Efficiency RPM 11,178 Amps 2.883 Stall Torque 1.543 G-CM

Once again thanks for taking the considerable time to look at my project.

Phill

[Subculture]

I don’t know what pitch the gears are on the Emaxx. Most car gears in the 1/8-10th scale are usually metric pitched and somewhere in the region of 0.7-1 mod in pitch. You can count the teeth and make a measurement of the external gear diameter to find out from charts what the pitch is assuming it isn’t imprinted on the gear itself.

Engel tanks use both 400 and 500 size motors, depending on the tank. Not sure why they mix and match so much, as a 400 size motor is more than sufficient to drive a 70mm piston, as you only need around 30 watts or so for moderate tank filling times.

Your existing gear train looks decent enough though, if the tanks are pulling a lot of current is that because of friction in the drive, too high revving motors or have you got a bit too much compression on your o-rings?

[Mermod]

Assuming your tanks are 70mm diameter like the Engel units, then something like these on the 1726RPM gearing, with an external 3:1 single stage to clear the spindle would do the job.

https://tinyurl.com/288x2mdw

Yep, 73mm ID, those geared units look really nice, I'll get onto ordering them ASAP, I'm guessing the 385 in the description means the motors a mabuchi 385 or similar, do the Engel units run a 385 or a 540?

Also do you have any good links to suitable gears for the final reduction? I think currently my final gear that is attached to the threaded insert is from a Traxxas Emaxx :)

Phill

[Subculture]

Assuming your tanks are 70mm diameter like the Engel units, then something like these on the 1726RPM gearing, with an external 3:1 single stage to clear the spindle would do the job.

https://tinyurl.com/288x2mdw

[Subculture]

Looks like a 919D, probably running on either an 11:1 or 6:1 ratio plus a further single stage reduction of around 3:1. Once again Norbert Bruggens book has a very acceptable formula for calculating wattage and gear ratios for a given piston tank, just basic Newtonian mechanics.

[Mermod]

I'm feeling that re-vamping my piston tanks just might be the best way to go despite being aluminium with "O" ring seals, I'm still glad I removed the watertight compartment as it was waaaay to heavily laid up, a new lighter variant looks to be the way to
Subculture I do like your idea of a planetary gearbox for more efficiency than what I currently have and the MFA ones are easily available here in Aus.
I'm a very visual kinda guy and I found this video on youtube which to me looks great, is around the same diameter and runs an MFA arrangement, only problem is I just cant make out the model number on it, would anyone have any ideas which one it might be?

https://www.youtube.com/watch?v=bTo3akHom6I

Thanks once again, Phill.

[Subculture]

Having two tanks half the length improves things quite a bit as you can see. Sadly another issue rears its ugly head if the tank is sealed- ensuring equal volume in each for correct longitudinal trim. The R&R twin pump system side steps this issue by locating the snorkel relief in the horizontal baffle, effectively acting as a limit switch for the pump.